LCD devices are widely applied in recent years because of the advantages of low power consumption, low manufacturing cost, no radiation, etc. As shown in FIG. 1, an LCD device mainly includes a backlight module 1, and an LCD panel 2; the backlight module 1 here is an edge-light backlight module of a bottom-light type, is a crucial thought for designing LCD devices with narrow frames, and can achieve the aim of the design of the minimum frame of 4.3 mm. Because a light guide panel 11 can generate heat expansion and cold contraction during operation, and has manufacturing tolerance, etc., a certain assembling gap is reserved between the end surface of the light guide panel 11 and a middle frame 12, resulting in light leakage. The light of a light source 3 is directly emitted from the aforementioned gap. Because the light is bright, bright line(s) may be formed at the frame of an LCD panel 2 after the light penetrates through an optical film 13, and local facula may be formed in severe conditions, causing the quality of the LCD device to decline.